JP3077362B2 - Optical disc reproducing method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing method and apparatus for reading a signal while irradiating an optical disk with a light beam, and more particularly to reproducing an optical disk having a signal surface formed of a phosphor. The present invention relates to a method and an apparatus for reproducing an optical disk when performing the operation.

[0002]

2. Description of the Related Art Optical recording media can be broadly classified into read-only media such as so-called compact discs and media capable of recording signals such as magneto-optical discs. However, it is desired to further increase the recording density. This is because when a digital video signal is considered as a signal to be recorded, the data amount needs to be several times to ten and several times that of a digital audio signal. This is because there is a demand for further reducing the size of the product such as a player by making the size smaller.
Also, a larger recording capacity is desired for general data disks.

[0003]

[Problems to be solved by the invention]

By the way, conventionally, when reproducing a signal recorded on an optical disk, for example, a laser beam is used as a light source, and the intensity of the laser beam reflected from the optical disk is detected by a photodetector. Signal reproduction is being performed.

At this time, the minimum reproducible signal interval (for example, signal pit interval) on the optical disk is λ ₁ depending on the numerical aperture (NA ₁ ) of the objective lens used in the optical pickup device and the wavelength (λ ₁ ) of the laser beam. / 2NA ₁ uniquely determined. For this reason, in order to increase the density of the optical disc, it is necessary to _first shorten the wavelength λ _{1 of the} light source (laser light) of the reproducing optical system and increase the numerical aperture NA ₁ of the objective lens. It has been. In addition,
FIG. 9 shows the reproduction signal characteristics of the conventional optical disk system with respect to the repetition frequency (spatial frequency) of the signal on the conventional optical disk.

As a method of reproducing a signal recorded on the optical disk, for example, a laser beam reflected from a signal surface of the optical disk is irradiated with a laser beam reflected at a confocal position with respect to the signal surface of the optical disk. Although there are also so-called confocal laser detection method for detecting using a photodetector having a light receiving portion of the size of the lower diameter or less, the opening of the also above likewise laser wavelength lambda ₁ and the objective lens in the confocal laser detection method The limit caused by the number NA ₁ cannot be exceeded.

Therefore, the present invention has been proposed in view of the above-described circumstances, and it has become possible to detect and reproduce a minute signal on an optical disk, which cannot be detected by a conventional optical disk system. It is an object of the present invention to provide a method and apparatus for reproducing an optical disk.

[0008]

SUMMARY OF THE INVENTION An optical disk reproducing method and apparatus according to the present invention have been proposed in order to achieve the above-mentioned object, and a signal surface on which a phosphor is applied in different states according to a signal to be recorded. When playing an optical disc with
By irradiating a laser beam condensed on the signal surface of the optical disk, and detecting fluorescence induced from the signal surface of the optical disk by the laser light on a confocal plane with respect to the signal surface of the optical disk, The signal on the optical disk is reproduced.

Further, in the optical disk reproducing method and apparatus according to the present invention, the laser light is wavelength-separated in the optical path of the reflected light from the optical disk, and the wavelength of the laser light is converted from the light detected on the confocal plane. I also try to remove the ingredients.

That is, in an optical disk system to which the present invention is applied, an optical pickup device that forms a signal on an optical disk with a phosphor and reproduces a signal from the optical disk includes a laser light source that generates a laser beam, An objective lens for condensing laser light from the laser light source on the signal surface of the optical disc, a condensing lens for collecting fluorescence induced by the laser light condensed and irradiated on the optical disc, And a photodetector arranged at the confocal position to detect the fluorescence collected by the condenser lens. The fluorescence induced from the signal surface of the optical disk by the laser light is arranged on the confocal surface. The signal on the optical disk is reproduced by detecting the detected light with the photodetector.

In the optical pickup device to which the present invention is applied, a wavelength separation filter is provided in the optical path of the reflected light from the optical disk, and the wavelength separation filter provides the laser in the optical path of the reflected light from the optical disk. The wavelength of the light is separated, and the wavelength component of the laser light is removed from the light detected by the photodetector arranged on the confocal plane.

Here, in the optical pickup device, the photodetector has a light receiving portion having a size equal to or smaller than a light spot diameter (re-imaging spot diameter) formed by fluorescence at the confocal position. .

Alternatively, the optical pickup device includes a pinhole having a diameter equal to or smaller than a light spot diameter at the confocal position, and a light receiving portion of a photodetector provided behind the pinhole detects light passing through the pinhole. To do.

Further, in the optical pickup device, a beam splitter is disposed between the laser light source and the objective lens, and the wavelength separation filter is disposed between the beam splitter and the photodetector. .

[0015]

According to the optical disk reproducing method and apparatus of the present invention, the fluorescence induced by the laser light focused and irradiated on the signal surface of the optical disk is detected on the confocal plane with respect to the signal surface of the optical disk. The signal on the optical disk is being reproduced.

Further, according to the optical disk reproducing method and apparatus of the present invention, the laser light is wavelength-separated in the optical path of the reflected light from the optical disk to remove this laser light wavelength component from the light detected on the confocal plane. Therefore, the detected light is only the fluorescence (signal) from the optical disk.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disk reproducing method and apparatus according to the present invention will be described below with reference to the drawings.

An optical disk reproducing method according to an embodiment of the present invention comprises:
This is an optical disk reproducing method for reproducing an optical disk having a signal surface formed of a phosphor FL as shown by a hatched portion in FIG. 1 or FIG.

Here, the optical disk having the signal surface shown in FIG. 1 can be prepared, for example, by the following steps. First, a light-sensitive material is applied thinly on an optical disk substrate, and the signal is recorded by irradiating a laser beam modulated according to a signal to be recorded onto the optical disk coated with the light-sensitive material. At this time, the photosensitive material is punched up to the disk substrate surface by the laser light. next,
A fluorescent material made of, for example, a high molecular compound such as a dye is applied on the disk surface of the photosensitive material punched by the laser light. As a result, the fluorescent material is applied to the surface of the photosensitive material and the disk substrate punched by the laser light. Then, the photosensitive material is dissolved and removed using a solvent. In this case, the fluorescent material other than the signal punched out by the laser light is also removed as the photosensitive material melts. Through the above steps, as shown in FIG. 1, it is possible to create an optical disc in which the signal region SG is formed in the remaining portion of the fluorescent material (phosphor FL).

The optical disk having the signal surface shown in FIG. 2 can be prepared, for example, by the following steps. First, apply a thin fluorescent material on the optical disc substrate,
The optical disk coated with the fluorescent material is irradiated with a laser beam modulated according to a signal to be recorded. At this time,
The fluorescent material applied on the optical disk substrate surface is vaporized by the heat of the laser light. As a result, as shown in FIG. 2, the signal region SG does not exist in the portion without the fluorescent material (phosphor FL).
It is possible to create an optical disk on which is formed.

That is, according to the optical disk reproducing method of the embodiment of the present invention, as described above, the fluorescent material FL is applied only to the signal area SG.
Using an optical disk (FIG. 1) in which the fluorescent material FL exists only in a portion other than the signal area SG (FIG. 1), and irradiating the laser light focused on the signal surface of the optical disk with the laser. A signal on the optical disk is reproduced by detecting fluorescent light (fluorescent light from the fluorescent material FL) induced from the signal surface of the optical disk by light on a confocal plane with respect to the signal surface of the optical disk. It is.

In the optical disk reproducing method according to the embodiment of the present invention, the wavelength of the laser light is separated from the light detected on the confocal plane by separating the wavelength of the laser light in the optical path of the reflected light from the optical disk. I also try to remove the ingredients.

The optical disk reproducing method according to the present invention will be described with reference to a specific configuration. In an optical disk system to which the optical disk reproducing method according to the present invention is applied, as shown in FIGS. As shown in FIG. 3, an optical pickup device that forms the area SG with the fluorescent material FL and reproduces the signal of the optical disk is shown in FIG.
Semiconductor laser L as laser light source for generating laser light
D, an objective lens OL for condensing the laser light from the semiconductor laser LD on the optical disc DK, and the laser light focused and irradiated on the optical disc DK by the objective lens OL to be induced from the phosphor FL. A condensing lens CL for collecting fluorescence, and a photodetector PD, which is a photodetector that is arranged at a confocal position with respect to the signal surface of the optical disc DK and detects the fluorescence collected by the condensing lens CL, Optical disk D by laser light
The signal on the optical disk is reproduced by detecting the fluorescence induced from the signal plane of K by the photodetector PD arranged on the confocal plane.

[0024] Here, the optical pickup device of the present embodiment, as shown in FIG. 4, the light receiving portion re _S of the photodetector PD, the light spot formed by the fluorescent fl confocal position (confocal plane rfp) It is assumed to have a size equal to or less than the diameter φ. Incidentally, the light receiving unit re _S is provided on the base bf photodetector PD.

Alternatively, as shown in FIG. 5, the photodetector PD of the optical pickup device includes a pinhole plate ph having a pinhole ho having a light spot diameter φ or less at the confocal position (confocal plane rfp). A light receiving unit re _L provided behind the pinhole ho (pinhole plate ph).
To detect the light passing through the pinhole ho (fluorescence fl).

Further, in the optical disk system to which the present invention is applied, a wavelength separation filter SF is provided in the optical path of the reflected light from the optical disk DK, and the wavelength separation filter SF is used in the optical path of the reflected light from the optical disk DK. the laser light is a wavelength separation of the light receiving portion of the photodetector PD disposed on the confocal plane rfp re _S or r
The wavelength component of the laser light is removed from the light detected by e _L.

Further, in the optical pickup device, a beam splitter BS is disposed between the semiconductor laser LD and the objective lens OL, and the wavelength separation filter SF is disposed between the beam splitter BS and the photodetector PD. Have been.

Hereinafter, the configuration of FIG. 3 will be specifically described.

In FIG. 3, a laser beam from a semiconductor laser LD, which is a laser light source, is applied to a collimator lens CO.
After being converted into parallel light by L, the light passes through the beam splitter BS and reaches the objective lens OL.
Is focused on the optical disk DK.

Signals are recorded on the signal surface of the optical disk DK as shown in FIG. 1 or FIG.
Therefore, the objective lens OL is provided on the optical disc DK.
By irradiating the laser light condensed by the above, fluorescent light proportional to the intensity of the laser light condensed by the objective lens OL is induced from the phosphor FL on the optical disc DK.

The induced fluorescence (fl) is collected through the objective lens OL and reaches the beam splitter BS. In the beam splitter BS, the fluorescent light passing through the objective lens OL is reflected, and the reflected fluorescent light reaches the wavelength separation filter SF.

The wavelength separating filter SF is an optical interference filter provided for removing the wavelength component of the laser light from the reflected light of the optical disk DK. For example, the wavelength separation filter SF has characteristics as shown in FIG. 6, and particularly, the wavelength λ _{1 of the} laser light.
Is low, and conversely, the transmittance is high at the wavelength λ ₂ of the fluorescence. The laser light is shielded by the wavelength separation filter SF.

The fluorescence passing through the wavelength separation filter SF is re-imaged on the light receiving surface of the photodetector PD by the condenser lens CL. Here, the re-imaging plane is a confocal plane with respect to the signal plane of the optical disc DK,
The spot diameter φ formed by the condenser lens CL is:
The numerical aperture NA ₂ of the condenser lens CL and the wavelength λ of the fluorescence
_{2, the} result is 1.22λ ₂ / NA ₂ .

[0034] In the photodetector PD in the present embodiment, for example, by using a light receiving portion re _S of the spot diameter φ following sizes as shown in FIG. 4 described above, to detect the fluorescence intensity. Alternatively, the confocal plane rfp as shown in FIG.
The fluorescence coming through the pinhole ho the spot diameter φ following sizes above are to be detected by the light receiving unit re _L.

Here, the reproduced signal characteristics when the optical disk system of the present embodiment is used will be described below. The reproduction signal level is calculated by the following equation (1).

[0036]

(Equation 1)

In the equation (1), P represents a pupil function on the objective lens, m represents a spatial frequency, and x ₂ and y ₂ represent coordinates on the photodetector PD. In the formula, * indicates a complex conjugate, and * indicates a convolution.

FIG. 7 shows the fluorescence wavelength dependence of the reproduction signal level with respect to the repetition frequency (spatial frequency) of the signal area (SG) formed on the optical disk DK.
Here, in FIG. 7, the spatial frequency axis is standardized by the conventional spatial frequency of the reproduction limit. Further, the photodetector size is assumed sufficiently smaller than the spot diameter (i.e., using the photo detector PD having a light receiving portion re _S in the example of FIG. 4). Further, FIG. 7 shows the reproduction signal level when the wavelength of the laser beam is λ ₁ and the fluorescence wavelength λ ₂ is, for example, λ ₁ , 2λ ₁ , 4λ ₁ . Generally, in the fluorescence phenomenon, the fluorescence wavelength λ ₂
Is larger than the laser wavelength λ ₁ , but the fluorescence wavelength λ ₂
Is desirably set to a wavelength as small as possible.

Next, FIG. 8 shows the dependence of the reproduction signal level on the photodetector size (the size of the light receiving portion of the photodetector PD) with respect to the repetition frequency (spatial frequency) of the signal area (SG) formed on the optical disk DK. Shows sex. In FIG. 8, the photodetector size α is, for example, λ ₂ / NA
Standardized in ₂ . According to FIG. 8, it is understood that an effective reproduction signal can be obtained when the photodetector size α is, for example, 1 or less. In the example of FIG. 8, and the fluorescence wavelength lambda ₂ for example, 1.1λ _1.

According to FIGS. 7 and 8 described above, by using a photodetector (light receiving section) having a size smaller than the spot diameter φ,
It enables reproduction of conventional signal beyond the spatial frequency of the reproduction limit, in particular, an effective under conditions where the fluorescence wave lambda ₂ is equal to or less than 4.lamda ₁ laser wavelength lambda _1. This also applies to the case where the pinhole ho is used.

As described above, in the optical disk system to which the optical disk reproducing method of this embodiment is applied, the optical disk DK having the signal surface formed by the fluorescent material FL is used, and the light is condensed by the objective lens OL. The fluorescence (fl) induced by the laser beam irradiated on the signal surface of the optical disk DK is reduced to a size smaller than the re-imaging spot diameter (φ) arranged on the confocal plane (rfp) in the optical pickup device. Photodetector (light receiving unit re _S )
Or the light (fl) passing through a pinhole (ho) having a light spot diameter (φ) or less provided at the confocal position (rfp) is detected by a photodetector (light receiving unit r).
The detection at e _L ) makes it possible to detect a small signal on the optical disk, which cannot be detected by the conventional optical disk system, thereby realizing a higher-density and larger-capacity optical disk system.

[0042]

As described above, according to the optical disk reproducing method and apparatus of the present invention, when reproducing an optical disk having a signal surface on which a phosphor is applied in a different state according to a signal to be recorded, the signal surface of the optical disk is reproduced. By detecting the fluorescence induced by the laser light condensed and irradiated on the confocal plane with respect to the signal plane of the optical disk, a small signal on the optical disk that could not be detected by the conventional optical disk system Can be detected and reproduced.

In the optical disk reproducing method and apparatus according to the present invention, the laser light is wavelength-separated in the optical path of the reflected light from the optical disk, and the wavelength of the laser light is converted from the light detected on the confocal plane with respect to the signal surface of the optical disk. By removing the component, only the fluorescence (signal) from the optical disk can be detected. Therefore, it is possible to detect and reproduce a minute signal on the optical disk which cannot be detected by the conventional optical disk system. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a signal surface of an optical disk used in an optical disk reproducing method of the present invention.

FIG. 2 is a diagram showing another example of the signal surface of the optical disc used in the optical disc reproducing method of the present invention.

FIG. 3 is a diagram showing a schematic configuration of an optical disk system to which the optical disk reproducing method of the present invention is applied.

FIG. 4 is a diagram illustrating a configuration of a main part of a photodetector having a light receiving unit having a size equal to or smaller than a spot diameter.

FIG. 5 is a diagram showing a configuration of a main part of a photodetector having a pinhole smaller than a spot diameter.

FIG. 6 is a characteristic diagram illustrating characteristics of a wavelength separation filter.

FIG. 7 is a characteristic diagram showing a fluorescence wavelength dependency of a reproduction signal level with respect to a spatial frequency.

FIG. 8 is a characteristic diagram showing a photodetector size dependency of a reproduction signal level with respect to a spatial frequency.

FIG. 9 is a characteristic diagram showing a reproduction signal level with respect to a signal repetition frequency (spatial frequency).

[Explanation of symbols]

 FL: Phosphor SG: Signal area LD: Semiconductor laser COL: Collimator lens BS: Beam splitter OL: Objective lens DK: ... Optical disk SF ... Wavelength separation filter CL ... Condenser lens PD ... Photodetector f1 ... Fluorescence re ... Light receiving unit ho ... Pinhole rfp ・ ・ ・ ・ ・ ・ Confocal plane φ ・ ・ ・ ・ ・ ・ Spot diameter

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Claims (4)

(57) [Claims] 1. An optical disk reproducing method for reproducing an optical disk having a signal surface in which a phosphor is applied differently according to a signal to be recorded, wherein the laser beam condensed on the signal surface of the optical disk is Irradiating the laser beam and detecting the fluorescence induced from the signal surface of the optical disk on the confocal plane with respect to the signal surface of the optical disk, thereby reproducing the signal on the optical disk; Method. 2. The method according to claim 1, wherein the wavelength of the laser light is separated in an optical path of the reflected light from the optical disk, and a wavelength component of the laser light is removed from the light detected on the confocal plane. An optical disk reproducing method according to claim 1. 3. An optical disk reproducing apparatus for reproducing an optical disk having a signal surface having a different phosphor application state according to a signal to be recorded, comprising: means for irradiating a laser beam focused on the signal surface of the optical disk; Means for detecting, on a confocal plane with respect to the signal surface of the optical disk, fluorescence detected by the laser light from the signal surface of the optical disk, thereby reproducing the signal on the optical disk. Optical disc playback device. 4. A device for separating a wavelength of the laser light in an optical path of a reflected light from the optical disk and removing a wavelength component of the laser light from light detected on the confocal plane. The optical disk reproducing device according to claim 3.